Organic-solvent-based photocurable resist composition and resist pattern-forming method

ABSTRACT

An organic solvent based photocurable resist composition containing a photopolymerizable polyurethane compound having a repeating unit represented by the following formula: B—[X] n [Y] m —B, where X is represented by the formula:                    
     and Y is represented by the formula: —OOCHN—A—NHCOO(R 2 )—, A is a structural unit derived from a polyisocyanate compound, B is same or different and a structural unit derived from a hydroxy compound having at least one photopolymerizable unsaturated group at molecular terminals respectively and optionally containing an ether linkage, R 1  is a structural unit derived from a carboxyl group-containing polyol compound, R 2  is a structural unit derived from a polyol compound, n is an integer of 1 to 10, m is an integer of 1 to 10, provided that one X and one Y are bonded to each other, or three or more of X and/or Y are bonded to each other.

FIELD OF THE INVENTION

The present invention relates to an organic solvent based photocurableresist composition, and particularly an organic solvent basedphotocurable resist composition for use in the preparation of a printedcircuit board. The organic solvent based photocurable resist compositionis applicable to a solder resist, etching resist, anti-plating resistand the like.

BACKGROUND ART

A method of forming a conductor circuit such as a printed circuit boardis known in the art, which comprises coating a photocurable resistcomposition onto a board, followed by exposing to light, developing toform a resist pattern, and by etching to remove unnecessary portion.

For example, a photocurable resist composition capable of beingdeveloped with a weak alkali by use of an unsaturated resin havingcarboxyl group is known as the above photocurable resist composition(see Japanese Patent Application Laid-Open No. 223759/91).

The above carboxyl group-containing unsaturated resin is usuallyprepared as described in the above prior art by a process whichcomprises subjecting an acid unsaturated monomer such as acrylic acidwith alkyl (meth)acrylate monomer to a radical copolymerization reactionto obtain a polycarboxylic acid resin, followed by subjecting the resinand an epoxy group-containing unsaturated monomer such as glycidyl(meth)acrylate to an addition reaction of a part of the carboxylgroup-containing alkyl (meth)acrylate monomer with glycidyl group.

The use of the above acid resin as an alkali development type resistcomposition had such problems (1) that a broad molecular weightdistribution of the acid resin prepared by the radical polymerizationreaction causes a reduction of solubility due to an alkali developingsolution or etching solution in a high molecular weight region and anincrease of solubility due to the alkali developing solution or etchingsolution in a low molecular weight region, resulting in making itimpossible to carry out a uniform developing treatment or etchingtreatment, (2) that difference of a radical copolymerization reactionspeed between a (meth)acrylic acid monomer component and alkyl(meth)acrylate monomer may produce a homopolymer of the acrylic acidmonomer or an acrylic resin containing the acrylic acid component in asmall amount, resulting in that formation of a fine resist pattern ismade impossible due to non-uniform speed of removing the resist film bythe alkali developing treatment, remaining of the resist film in a shortperiod of treating time, and to erosion and washing out of a photocuredfilm, (3) that heating on the addition reaction between thepolycarboxylic acid resin and the epoxy group-containing unsaturatedmonomer further increases molecular weight of the polycarboxylic acidresin, (4) that unnecessary presence with the resin of a radicalpolymerization inhibitor usually added for the purpose of inhibiting theradical polymerization reaction unsaturated groups on the additionreaction reduces reactivity of the photopolymerization reaction, and (5)that erosion and washing out of the photocured film by the etchingsolution due to unsatisfactory properties of the photocured film makesit impossible to form a fine resist pattern.

As a method of introducing an unsaturated group into the resin, inaddition to the above method, for example, Japanese Patent ApplicationLaid-Open No. 102037/95 discloses a process for preparing awater-soluble actinic radiation-curable resin which comprises reacting apolyhydroxy compound, radically polymerizable unsaturatedgroup-containing polyhydroxy compound, anionic hydrophilicgroup-containing polyhydroxy compound, polyisocyanate compound andradically polymerizable unsaturated group-containing monohydroxycompound to obtain a polyurethane resin, followed by neutralizing withan amine. However, use of the above water-soluble polyurethane resin asa resist composition produced such problems that poor alkali developingproperties and anti-etching properties make it impossible to form a fineresist pattern.

As another method of introducing an unsaturated group into the resin,Japanese Patent Application Laid-Open No. 136077/94 discloses aradiation-curable resin composition prepared by reacting a reactionproduct of dimethylol propionic acid with ε-caprolactone, organicpolyisocyanate compound and hydroxyl group-containing (meth)acrylate.However, use of the above resin composition as the resist compositionhad problems of poor properties in alkali developing properties,anti-ethcing properties and the like.

DESCLOSURE OF THE INVENTION

The present inventors made intensive studies to solve the above problemsto find out that a specified organic solvent based photocurable resistcomposition shows good properties in an alkali developing properties,anti-etching resist properties, etc., and has such a good performancesas to form a fine resist pattern, resulting in completing the presentinvention.

That is, the present invention provides an organic solvent basedphotocurable resist composition containing a photopolymerizablepolyurethane compound having a repeating unit represented by thefollowing formula; B—[X]_(n)[Y]_(m)—B₁, where X is represented by theformula:

and Y is represented by the formula: —OOCHN—A—NHCOO—(R₂)—, A is astructural unit derived from a polyisocyanate compound, B is same ordifferent and a structural unit derived from a hydroxy compound havingat least one photopolymerizable unsaturated group at molecular terminalsrespectively and optionally containing an ether linkage, R₁ is astructural unit derived from a carboxyl group-containing polyolcompound, R₂ is a structural unit derived from a polyol compound, n isan integer of 1 to 10, m is an integer of 1 to 10, provided that one Xand one Y are bonded to each other, or three or more of X and/or Y arebonded to each other.

Preferable Embodiment of the Invention

The organic solvent based photocurable resist composition of the presentinvention is explained hereinafter. Respective compounds, from whichrespective structural units in the above formulas are formed, are apolyisocyanate compound, hydroxy compound having at least onephotopolymerizable unsaturated group at molecular terminals, carboxylgroup-containing polyol compound and polyol compound respectively. Thesecompounds are explained hereinafter.

The polyisocyanate compound is used for bonding a compound introducingcarboxyl group into the molecule to a compound introducingphotopolymerizable unsaturated group at molecular terminals.

The polyisocyanate compound may include aliphatic diisocyanate compoundsuch as hexamethylene diisocyanate, trimethylenediisocyanate,1,4-tetramethylene-diisocyanate, pentamethylenediisocyanate,1,2-propylenediisocyanate, 1,2-butylenediisocyanate,trimethylhexamethylene diisocyanate, dimer acid diisocyanate,lysinediisocyanate, 2,3-butylenediisocyanate, 1,3-butylene-diisocyanateand the like; alicyclic diisocyanate compound such asisophoronediisocyanate, 4, 4′-methylene bis(cyclohexylisocyante),methylcyclohexane-2,4-(or -2,6-) diisocyanate, 1,3-(or1,4-)-di(isocyanatomethyl)cyclohexane, 1,4-cyclohexanediisocyanate,1,3-cyclopentanediisocyanate, 1,2-cyclohexanediisocyanate and the like;aromatic diisocyanate compound such as xylyenediisocyanate, m-xylylenediisocyanate, tetramethylxylyenediisocyanate, tolylenediisocyanate,4,4′-diphenyl-methanediisocyanate, 1,5-naphthalenediisocyanate,1,4-naphthalenediisocyanate, 4,4′-toluidinediisocyanate,4,4′-diphenyletherdiisocyanate, (m- or p-) phenylenediisocyanate,4,4′-biphenylenediisocyanate,3,3′-dimethyl-4,4′-biphenylenediisocyanate, bis(4-isocyanatophenyl)sulfone, isopropylidene bis(4-phenylisocyanate) and the like; otherpolyisocyanates, for example, polyisocyanate compounds having three ormore isocyanate group such as triphenylmethane -4,4′,4″-triisocyanate,1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene,4,4′-dimethyidiphenylmethane -2,2′,5,5′-tetraisocyanate and the like,adducts prepared by reacting a polyol such as ethylene glycol, propyleneglycol, 1,4-butylene glycol, polyalkylene glycol, trimethylolpropane,hexanetriol and the like with a polyisocyanate compound in an excessamount of isocyanate group relative to hydroxy group in the polyol,biuret type adducts of hexamethylenediisocyanate,isophoronediisocyanate, tolylenediisocyanate, xylenediisocyanate,4,4′-diphenylmethanediisocyanate, 4,4′-methylenebis(cyclohexylisocyanate) and the like, isocyanuric ring type adducts,and the like. These compounds may be used alone or in combination. Ofthese, aromatic diisocyanate compounds are preferable, because thearomatic diisocyanate compound is hardly hydrolyzed to the alkalideveloping solution and is capable of forming a photocured film, whichhas high resistance to the alkali developing solution and etchingsolution, and which is so tough as to be sufficiently adhered withoutbeing separated from the substrate by an external force such as theetching solution and the like until the photocured resist film isremoved from the resist pattern forming method.

The hydroxy compound having at least one photopolymerizable unsaturatedgroup at molecular terminals is a compound used for introducing thephotopolymerizable unsaturated group to the molecular terminals.

The photopolymerizable unsaturated group is an unsaturated group whichis subjected to a radical polymerization reaction by light to form acrosslinked structure and may include unsaturated groups known in theart. Of these, (meth)acryloyl group is particularly preferable.

The hydroxy compound may include ones prepared by reacting one mole ofpolyhydric alcohol with one mole or more of an unsaturated acid so thathydroxyl group may remain after reaction. Specific examples thereof mayinclude hydroxy compounds containing respectively one unsaturated groupin one molecule of hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxymethyl (meth)acrylate, (poly)ethylene glycolmono(meth)acrylate, (poly)propylene glycol mono(meth)acrylate,1,6-hexanediol mono(meth)acrylate and the like; hydroxy compoundscontaining respectively two or more unsaturated groups in one moleculeof glycerine di(meth)acrylate, diglycerine di(meth)acrylate, diglycerinetri(meth)acrylate, trimethylolpropane (meth)acrylate, pentaerythritol(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritoldi(meth)acrylate, hydroxyisocyanurate di(meth)acrylate, sorbitoldi(meth)acrylate and the like; and the like. These may be used alone orin combination. Of these, the hydroxy compounds containing two or moreof unsaturated group are preferable.

The carboxyl group-containing polyol compound is such that introductionof carboxyl group into the molecule makes it possible to remove anon-irradiated resist film by the alkali developing treatment.

The carboxyl group-containing polyol compound may include compoundscontaining at least one carboxyl group and two or more hydroxy groups inthe molecule. Specific examples thereof may include, for example,semiester compounds prepared by reacting 2,2-dimethylol propionic acid,2,2-dimethylol acetic acid, 2,2-dimethylol pentanic acid, or triolcompounds with an acid anhydride; sulfonate diol compounds prepared bysubjecting sodium dimethylsulfoisophthalate and glycols to esterexchange reaction in the presence of an excess amount of the glycols;and the like. These may be used alone or in combination.

In the above formulas representing the photopolymerizable polyurethanecompound, n is in the range of 1 to 10, preferably 1 to 5. When n isless than 1, the alkali developing treatment is made impossible. When nis more than 10, a resist sensitivity and the like may be reduced.Usually, the photopolymerizable polyurethane compound has a numberaverage molecular weight in the range of about 1000 to 20000.

The polyol compound is such that a hydrophobic group free of carboxylgroup in the molecule is introduced into a molecular backbone so as tocontrol a balance between hydrophilic properties and hydrophobicproperties in the polyurethane compound. On the other hand, polyalkyleneglycol having a number average molecular weight in the range of about500 to 5000 or the like per se provides hydrophilic properties, and isalso capable of imparting flexibility to the resist film, resulting inimproving film performances in alkali developing properties,anti-etching properties, etc.

The polyol compound may include compounds containing at least twohydroxy groups in the molecule. Specific examples thereof may include(poly)methylene glycol, (poly)ethylene glycol, (poly)propylene glycol,1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol,3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol,1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol3-methyl-3,4-pentanediol, 3-methyl-4,5-pentanediol,2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol,1,4-hexanediol, 2,5-hexanediol, 1,4-cyclohexanediol, neopentyl glycol,pentaerythritol, trimethylol propane, glycerol and the like. These maybe used alone or in combination. Of these, the hydroxy compoundcontaining two hydroxy groups in one molecule is preferable.

The photopolymerizable polyurethane compound may be prepared by the sameprocess as in the general polyurethane resin. That is, thephotopolymerizable polyurethane compound may be prepared by a processwhich comprises subjecting a mixture of a carboxyl group-containingpolyol compound, polyol compound and polyisocyanate compound at such anexcess amount of polyisocyanate group that an isocyanate group tohydroxy group molar ratio is in the range of about 2.0 to 1.1,preferably about 2.0 to 1.2, to addition reaction between isocyanategroup and hydroxy group to prepare a carboxyl group-containingisocyanate compound, followed by subjecting a mixture of the carboxylgroup-containing isocyanate compound with a photopolymerizableunsaturated group-containing polyol compound at such a mixing ratio thatan isocyanate group to hydroxy group molar ratio is in the range ofabout 0.8 to 1.0, preferably about 0.9 to 1.0, to addition reaction.Otherwise, the carboxyl group may be esterified with lower alcohol suchas methanol, ethanol, propanol and the like to be blocked prior to theabove addition reaction, followed by heating after reaction to removethe lower alcohol for regenerating the carboxyl group.

The addition reaction between isocyanate group and hydroxy group may becarried out at a reaction temperature usually in the range of 50 to 150°C., but preferably 1000° C. or lower so as to prevent polymerization ofradically polymerizable unsaturated group. If needed, anurethane-forming reaction catalyst may be used. The urethane-formingreaction catalyst may include organotin compounds such as tin octylate,dibutyltin dilaurate and the like. In the preparation of thepolyurethane resin, an organic solvent may optionally be used. Examplesof the organic solvent may include acetone, methyl ethyl ketone, methylisobutyl ketone, ethyl acetate, butyl acetate, toluene, xylene,N,N-dimethylformamide, N-methyl-2-pyrrolidone and the like.

The light defined in the present invention may include actinic radiationsuch as electron rays, ultraviolet light, visible light and the like. Inthe case where crosslinking is carried out by irradiation of ultravioletlight or visible light, a radical photopolymerization initiator andoptionally a photosensitizer may also be added.

The radical photopolymerization initiator may include ones known in theart, for example, aromatic carbonyl compounds such as benzophenone,benzoin methyl ether, benzoin isopropyl ether, benzylxanthone,thioxanthone, anthraquinone and the like; acetophenones such asacetophenone, propiophenone, α-hydroxyisobutylphenone,α,α′-dichloro-4-phenoxyacetophenone, 1-hydroxy-1-cyclohexylacetophenone,diacetylphenone, and the like; organic peroxides such as benzoylperoxide, t-butylperoxy-2-ethylhexanoate, t-butylhydroperoxide,di-t-butyl-diperoxyisophtharate, 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophene and the like; diphenyl halonium saltssuch as diphenyliodonium bromide, diphenyliodonium chloride and thelike; organohalides such as carbon tetrabromide, chloroform, iodoformand the like; heterocyclic and polycyclic compounds such as3-phenyl-5-isooxazolone, 2,4,6-tris(trichloromethyl)-1,3,5-triazinebenzanthrone and the like; azo compounds such as 2,2′-azo(2,4-dimethylvaleronitrile), 2,2-azobisisobutylonitrile,1,1′-azobis(cyclohexane-1-carbonitrile),2,2′-azobis(2-methylbutylonitrile) and the like; iron-allene complex(see European Patent No. 152377), titanocene compounds (see JapanesePatent Application Laid-Open No. 221110/88), bisimidazole basedcompounds; N-arylglycidyl based compounds; acridine based compounds;combinations of aromatic ketone with aromatic amine; peroxyketal (seeJapanese Patent Application Laid-Open No. 321895/94) and the like. Ofthe above radical photopolymerization initiators,di-t-butyidiperoxyisophthalate, 3,3′4,4′-tetra (t-butylperoxycarbonyl)benzophenone, iron-allene complex and titanocene compound are preferablebecause of high activity on crosslinking or polymerization.

Trade names of the radical photopolymerization initiator may includeIrgacure 651 (marketed by Ciba Geigy Limited, trade name, acetophenonebased radical photopolymerization initiator), Irgacure 184 (marketed byCiba Geigy Limited, trade name, acetophenone based radicalphotopolymerization initiator), Irgacure 1850 (marketed by Ciba GeigyLimited, trade name, acetophenone based radical photopolymerizationinitiator), Irgacure 907 (marketed by Ciba Geigy Limited, trade name,aminoalkylphenone based radical photopolymerization initiator), Irgacure369 (marketed by Ciba Geigy Limited, trade name, aminoalkylphenone basedradical photopolymerization initiator), Lucirin TPO (marketed by BASFLtd., trade name, 2,4,6-trimethylbenzoyl diphenylphosphine oxide),Kayacure DETXS (marketed by Nippon Kayaku Co., Ltd., trade name),CGI-784 (marketed by Ciba Geigy Limited, trade name, titanium complexcompound), and the like. These may be used alone or in combination.

Examples of photosensitive dyes may include ones based on thioxanthene,xanthene, ketone, thiopyrylium salt, base styryl, merocyanine,3-substituted coumarine, 3,4-substituted coumarine, cyanine, acrydine,thiazine, phenothiazine, anthracene, coronene, benzanthracene, perylene,merocyanine, ketocoumarine, fumarine, borate, and the like. These may beused alone or in combination. The borate based photosensitive dyes mayinclude ones disclosed in, for example, Japanese Patent ApplicationLaid-Open Nos. 241338/93, 5685/95 and 225474/95.

The photopolymerizable composition of the present invention optionallycontain other unsaturated compounds, adhesion promotors, polymerizationinhibitors such as hydroquinone, 2,6-di-t-butyl-p-cresol,N,N-diphenyl-p-phenylene diamine and the like, organic resin fineparticles of saturated resin, unsaturated group-containing vinyl polymerand the like, pigments such as color pigment, extender pigment and thelike, metallic oxides such as cobalt oxide and the like, plasticizerssuch as dibutyl phthalate, dioctyl phthalate, tricresyl phosphate,polyethylene glycol, polypropylene glycol and the like, cissinginhibitor, flowability controlling agent, and the like.

The other unsaturated compound may include, for example, a compoundhaving preferably 1 to 4 radically polymerizable unsaturated groups, andmonomer, dimer, trimer and other oligomers which insolubilize an exposedarea by addition polymerization on exposure. Specific examples of thesecompounds may include acrylic acid, methacrylic acid, ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, tetra or more (4-16) polyethylene glycoldi(meth)acrylate, propylene glycol di(meth)acrylate, trimethylol propanetri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethylene glycoldiitaconate, ethylene glycol dimaleate, hydroquinone di(meth)acrylate,resorcinol di(meth)acrylate, pyrogallol (meth)acrylate, oligourethaneacrylate, oligoepoxy acrylate, divinyl benzene and the like. The aboveethylenicaly unsaturated compounds may be used alone or in combination.

An amount of the ethylenically unsaturated compound is usually in therange of 200 parts by weight or less, preferably 3 to 50 parts by weightper 100 parts by weight of the photopolymerizable urethane compound.

The above adhesion promotor is used for improving adhesion of thecoating film to the base board, and may include, for example, tetrazolessuch as tetrazole, 1-phenyltetrazole, 5-aminotetrazole,5-amino-1-methyltetrazole, 5-amino-2-phenyltetrazole,5-mercapto-1-phenyltetrazole, 5-mercapto-1-methyltetrazole,5-methylthiotetrazole, 5-chloro-1-phenyl-1H-tetrazole, and the like.These may be used alone or in combination.

The above saturated resin may be used for controlling solubility of thephotocurable resist composition, that is, may be used as an inhibitorfor solubility of the resist film in the alkali developing solution, orfor solubility in a strong alkali solution, for example, used in removalof the photocured film. Examples thereof may include polyester resin,alkyd resin, (meth) acrylic resin, vinyl resin, epoxy resin, phenolresin, natural resin, synthetic rubber, silicone resin, fluorocarbonresin, polyurethane resin, and the like. These may be used alone or incombination.

The unsaturated resin may preferably include ones having about 1 to 10on an average, particularly about 1 to 4 unsaturated groups in onemolecule of the above resin.

An amount to be used of the saturated or unsaturated resin is generallyin the range of 200 parts by weight or less, preferably 3 to 50 parts byweight per 100 parts by weight of the photopolymerizable polyurethanecompound.

The photocurable resist composition of the present invention isapplicable to wide uses, as photocurable materials known in the art, forexample, coating composition, ink, adhesive, resist material, printingmaterials such as photoengraving material for use in lithography orletterpress printing, PS plate for use in offset printing, informationrecording material, relief image-forming material and the like,particularly as the resist composition.

The photocurable resist composition may be used as an organic solventbased resist, as it is, and may be coated onto a base film to be used ina dry film resist.

The organic solvent based resist may be prepared by dissolving ordispersing the photocurable resist composition into an organic solventsuch as ketones, esters, ethers, cellosolves, aromatic hydrocarbons,alcohols, halogenated hydrocarbons and the like.

The above composition may be coated onto a substrate, for example, asheet of metals such as aluminum, magnesium, copper, zinc, chrome,nickel, iron and the like or of alloys comprising the above metals, aprinted circuit board surface-treated with the above metals, plastic,glass, silicone wafer, carbon, etc. by a coating method such as roller,roll coater, spin coater, curtain roll coater, spray, electrostaticcoating, dip coating, silk screen printing and the like, followed byoptional setting, and drying to obtain a photocurable resist film.

The surface of the photocurable resist film may be covered with a covercoat layer prior to being exposed to light for curing. The above covercoat layer may be used as a barrier to oxygen in air so thatdeactivation by oxygen of radicals generated on exposure to light may becontrolled, resulting in smoothly proceeding curing of photocurablematerials by exposure to light.

The cover coat layer may be formed by covering the surface of a coatingfilm with a resin film having a film thickness of about 1 (one) to 70 μmand formed from polyester resin such as polyethylene terephothalate andthe like, acrylic resin, polyethylene, polyvinyl chloride resin and thelike, or by coating to be a dry film thickness of about 0.5 to 5 μm ontothe surface of a coating film an aqueous solution prepared by dissolvingor dispersing into water aqueous resins from polyvinyl alcohol,partially saponified product of polyvinyl acetate, polyvinylalcohol-vinyl acetate copolymer, partially saponified polyvinylacetate-vinyl acetate copolymer, polyvinyl pyrrolidone, water-solublepolysuccharides polymers such as plurane and the like, respectivelybasic group, acid group or salt-containing acrylic resin, polyesterresin, vinyl resin, epoxy resin and the like, followed by drying. Thecover coat layer may preferably be removed after exposure of the surfaceof the photocurable material to light and prior to the developingtreatment. The cover coat layer of the water-soluble polysaccharidespolymer or the aqueous resin may be removed with a solvent capable ofdissolving or dispersing the above resins, for example, water, aqueousacid solution, aqueous basic solution and the like.

The dry film resist is prepared by a process which comprises coating theorganic solvent based resist composition onto a transparent resin filmconstituting a base film layer and formed from polyester resin such aspolyethylene terephthalate and the like, acrylic resin, polyethylene,polyvinyl chloride resin and the like by use of a roll coater, bladecoater, curtain flow coater and the like, followed by drying to form aphotocurable resist film having a dry film thickness of 0.5 to 50 μm,particularly 1 to 15 μm, and applying a protective film onto the surfaceof the photocurable resist film.

The dry film resist may be used for forming a photocurable resist filmonto the above-mentioned substrate by removing the protective film,followed by adhering the photocurable resist film to the above substrateso that the photocurable resist film may face to the substrate by athermocompression bonding method and the like. The resultingphotocurable resist film is then exposed to light and cured depending ona predetermined printed image after removing or without removing thebase film layer, followed by subjecting to a developing treatmentdirectly or after removing the base coat layer as the case may be toform the printed image. In the dry film resist, optionally theabove-mentioned cover coat layer may be applied between the base filmlayer and the photocurable resist film. The cover coat layer either maybe coated or adhered onto the photocurable resist film. The cover coatlayer either may be removed or may not be removed prior to thedeveloping treatment.

A light source to be used in photocuring may include, for example,respectively ultrahigh pressure, high pressure, moderate pressure, lowpressure mercury lamps, chemical lamp, carbon arc lamp, xenone lamp,metal halide lamp, tungsten lamp and the like, and various lasers havingan oscillating curve in a visible light region. Of these, argon laserhaving an oscillating curve in 488 nm and YAG-SHG laser having anoscillating curve in 532 nm are preferable.

The photocurable resist composition of the present invention may becoated or printed onto a substrate, for example, a plastic sheet, metal,glass, paper wood and the like. The above composition may preferably beused for forming a resist pattern film.

The method of forming the resist pattern onto the substrate by use ofthe above photocurable resist composition is explained hereinafter.

The resist pattern may be formed by a method which comprises (1) coatingthe organic solvent based photocurable resist composition onto asubstrate to form a photocurable resist film, (2) exposing thephotocurable resist film directly to a laser beam or through a negativemask to light for curing so that a resist film having a predeterminedprinted image can be obtained, and (3) subjecting the photocurableresist film to an alkali developing treatment, and removing a non-curedarea of the phoptocurable resist film with an aqueous alkali solution toform a resist pattern on the substrate. Thereafter, a copper layer notcovered with the resist film may removed by etching, followed byremoving the resist film to obtain a conductor pattern.

Examples of the substrate may include electrical insulating plastic filmor plastic plate such as glass-epoxy resin plate, polyethyleneterephthalate film, polyimide film and the like; ones prepared byforming an electrically conductive film, for example, by adhering ametal foil of copper, aluminum and the like, or by subjecting metalssuch as copper, nickel, silver and the like or compounds such aselectrically conductive oxides such as indium tin oxide (ITO) and thelike to vacuum metallizing, chemical metallizing, plating and the likeonto the surface of the above plastic plate or plastic film; conesprepared by forming an electrically conductive film on the surface of aplastic plate or plastic film having a through hole or on the throughhole; metal plate such as copper plate and the like, and the like.

In the coating step (1), the photocurable resist composition is coatedonto the surface of the substrate by a coating method such as spraycoating, electrostatic coating, spin coating, dip coating, rollercoating, curtain flow coating, silk screen printing and the like,followed by optionally setting, and by drying at a temperature in therange of about 50 to 130° C. to form a photocurable resist film. Theresulting photocurable resist film is exposed to light in the followingstep (2), in which a non-photocurable cover coat known in the art mayoptionally be applied onto the surface of the photocurable resist filmas a barrier to oxygen for preventing inhibition of curing of thephotocurable resist film by exposure to light.

The light source used in the above step (2) of exposing to light maypreferably include visible light practically used and having a wavelength in an emission spectrum of the light of 488 nm as an argon laseror 532 nm as a YAG-SHG laser without being limited thereto.

The washing out of the non-cured resist film in the step (3) of thedeveloping treatment may be carried out by use of an aqueous weak alkalisolution prepared by diluting caustic soda, sodium carbonate, causticpotash, ammonia, amine and the like with water. In the case where thecover coat is used, the cover coat may preferably be removed prior tothe developing treatment.

In the case where the resist pattern is used as an etching resist base,an exposed and non-circuit copper layer in the resist pattern may beremoved by etching by use of an aqueous solution of ferric chloride orcupric chloride. Removal of the resist film may be carried out by use ofa strong alkali such as caustic soda and the like or a solvent such asmethyl chloride and the like.

The base having the resist pattern may be used as decoration, solderresist base and etching resist base.

EXAMPLE

The present invention is explained more in detail by the followingExamples, in which “part” and “%” represent “part by weight” and “% byweight” respectively.

Preparation of Photocurable Resist Composition Example 1

Photopolymerizable polyurethane

Compound A (*) 100 parts Polymerization initiator (**) 3 partsPhotosensitizer (***) 1.5 parts Ethyl acetate 400 parts

The above formulation was mixed to prepane a photocurable resistcomposition of Example 1.

(*) photopolymerizable polyurethane compound A: an addition product of areaction product of one mole of dimethylol butyric acid, one mole ofpolyethylene glycol having a number average molecular weight of 2000 and3 moles of xylylene diisocyanate with 2 moles of trimethylopropanediacrylate as represented by the following formula:

(**) Polymerization initiator: titanocene compound, trade name, CGI-784,marketed by Ciba Geigy Limited.

(***) Photosensitizer LS-1: coumarin based photosensitizer, trade name,NKX-1595, Nippon Kankoshikiso Co., Ltd.

The photocurable composition obtained as above was coated by a barcoater onto a copper-clad glass fiber-reinforced epoxy resin base havinga copper layer of 18 μm on its surface, a base thickness of 2 mm and asize of 350×460 mm, followed by drying at 60° C. for 10 minutes toobtain a photocurable resist film having a dry film thickness of 10 μm.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [Line (μm)/space (μm)] in an irradiation dose of 5 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 60° C. for 10minutes, dipping into a 1% sodium carbonate aqueous solution at 30° C.for one minute to carry out an alkali developing treatment for removingthe non-cured area of the photocurable resist film, resulting in forminga resist pattern having a good resolution of 100 μm/100 μm, carrying outetching by dipping into an aqueous 24% ferrice chloride solution at 20°C. for 2 minutes to remove an exposed copper layer, resulting inobtaining a good resolution of 100 μm/100 μm.

Example 2

Example 1 was duplicated except that the following photopolymerizablepolyurethane compound (B) (*) was used in place of thephotopolymerizable polyurethane compound A in Example 1 to prepare aphotocurable composition of Example 2 as represented by the followingformula:

(*) Photopolymerizable polyurethane compound B: an adduct of a reactionproduct of one mole of dimethylol butyric acid, one mole of propyleneglycol (number average molecular weight: 1000) and 3 moles of xylylenedisocyanate with 2 moles of trimethylolpropane diacrylate. Thephotocurable composition of Example 2 was subjected to the sameprocedures as in Example 1 to form a photocurable resist film on theepoxy resin base.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [line (μm)/space (μm)] in an irradiation dose of 5 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 60° C. for 10minutes, dipping into a 1% sodium carbonate aqueous solution at 30° C.for one minute to carry out an alkali developing treatment for removingthe non-cured area of the photocurable resist film, resulting in forminga resist pattern having a good resolution of 100 μm/100 μm, carrying outetching by dipping into an aqueous 24% ferric chloride solution for 2minutes to remove an exposed copper layer, resulting in obtaining a goodresolution of 100 μm/100 μm.

Example 3

Example 1 was duplicated except that the following photopolymerizablepolyurethane compound (C)(*) was used in place of the photopolymerizablepolyurethane compound A in Example 1 to prepare a photocurablecomposition of Example 3 as represented by the following formula:

(*) Photopolymerizable polyurethane compound C: an adduct of a reactionproduct of one mole of dimethylol butyric acid, one mole of1,5-pentanediol and 3 moles of xylylene diisocyanate with 2 moles oftrimethylolpropane diacrylate.

The photocurable composition of Example 3 was subjected to the sameprocedures as in Example 1 to form a photocurable resist film on theepoxy resin base.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [line (μm)/space (μm)] in an irradiation dose of 5 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 60° C. for 10minutes, dipping into a 1% sodium carbonate aqueous solution at 30° C.for one minute to carry out an alkali developing treatment for removingthe non-cured area of the photocurable resist film, resulting in forminga resist pattern having a good resolution of 100 μm/100 μm, carrying outetching by dipping into an aqueous 24% ferric chloride solution at 20°C. for 2 minutes to remove an exposed copper layer, resulting inobtaining a good resolution of 100 μm/100 μm.

Example 4

A polymerization initiator A, i.e. Irgacure 907 and a polymerizationinitiator B, i.e. Kayacure DETX-S were used in place of thepolymerization initiator, CGI-284 and the photosensitizer NKX-1595 inExample 1 to obtain a photocurable composition of Example 4.

Photopolymerizable polyurethane 100 parts compound A Polymerizationinitiator A (****) 10 parts Polymerization initiator B (*****) 2 partsEthyl acetate 400 parts

The above formulation was mixed to-prepare a photopolymerizablecomposition of Example 4.

(****) Polymerization initiator A: aminoalkylphenone based photoradicalpolymerization initiator, trade name, Irgacure 907, marketed by CibaGeigy Limited.

(*****) Polymerization initiator B: thioxanthone based photoradicalpolymerization initiator, trade name, Kayacure DETX-S, marketed byNippon Kayaku Co., Ltd.

The photopolymerizable composition obtained as above was coated by a barcoater onto a copper-clad glass fiber-reinforced epoxy resin base havinga copper layer of 18 μm on its surface, a base thickness of 2 mm and asize of 350×460 mm, followed by drying at 60° C. for 10 minutes toobtain a photocurable resist film having a dry film thickness of 10 μm,

A light was irradiated onto the photocurable resist film-formed epoxyresin base so as to result a resolution of 100 μm/100 μm [line(μm)/space (μm)] in an irradiation dose of 100 mj/cm² by use of anultrahigh pressure mercury lamp, followed by heating the photocurableresist-formed epoxy resin base at 60° C. for 10 minutes, dipping into a1% sodium carbonate aqueous solution at 30° C. for one minute to carryout an alkali developing treatment for removing the non-cured area ofthe photocurable resist film, resulting in forming a resist patternhaving a good resolution of 100 μm/100 μm, carrying out etching bydipping into an aqueous 24% ferric chloride solution for 2 minutes toremove an exposed copper layer, resulting in obtaining a good resolutionof 100 μm/100 μm.

Example 5

In place of the photocurable resist composition of Example 2, a colorpigment, extender pigment, curing agent, etc. were added to obtain aphotocurable solder resist composition of Example 5.

Photopolymerizable polyurethane 100 parts compound A Polymerizationinitiator A (****) 5 parts Polymerization initiator B (*****) 1 partPhthalocyanine green 1 part Talc 50 parts Epoxy resin (******) 20 partsEthyl acetate 100 parts

The above formulation was dispersed and mixed to prepare aphotopolymerizable composition of Example 5.

(****) Polymerization initiator A: aminoalkylphenone based photoradicalpolymerization initiator, trade name, Irgacure 907, marketed by CibaGeigy Limited.

(*****) Polymerization initiator B: thioxanthone based photoradicalpolymerization initiator, trade name, Kayacure DETX-S, marketed byNippon Kayaku Co., Ltd.

(******) Epoxy resin: bisphenol A type liquid epoxy resin, trade name,Epikote 828, marketed by Yuka Shell Co., Ltd.

The photopolymerizable composition obtained as above was coated by a barcoater onto a copper-clad glass fiber-reinforced epoxy resin base havinga copper layer of 18 μm on its surface, a base thickness of 2 mm and asize of 350×460 mm, followed by drying at 80° C. for 10 minutes toobtain a photocurable resist film having a dry film thickness of 50 μm.

A light was irradiated onto the photocurable resist film-formed epoxyresin base so as to result a resolution of 100 μm/100 μm [line(μm)/space (μm)] in an irradiation dose of 100 mj/cm² by use of anultrahigh pressure mercury lamp, followed by dipping into a 1% sodiumcarbonate aqueous solution at 30° C. for one minute to carry out analkali developing treatment for removing the non-cured area of thephotocurable resist film, resulting in forming a resist pattern having agood resolution of 100 μm/100 μm.

Comparative Example 1

A mixture of 40 parts of methyl methacrylate, 40 parts of butylacrylate, 20 parts of acrylic acid and 2 parts of azobisisobutyronitrilewas dropped into 90 parts of propylene glycol monomethyl ether at 100°C. over 3 hours under nitrogen atmosphere. Completion of dropping wasfollowed by aging for one hour, dropping a mixture of one part ofazobisdimethylvaleronitrile and 10 parts of propylene glycol monomethylether over one hour, aging for 5 hours to obtain a high acid valueacrylic resin (resin acid value: 155 mgKOH/g) solution, adding 24 partsof glycidyl methacrylate, 0.12 part of hydroquinone and 0.6 part oftetraethylammonium bromide, and reacting at 100° C. for 5 hoursintroducing air to obtain a photocurable resin solution having a solidcontent of about 55.4%. The resulting resin had a resin acid value ofabout 50 mgKOH/g and a number average molecular weight of about 20,000.

Example 1 was duplicated except that the above photocurable resinsolution was used in place of the photopolymerizable polyurethanecompound A in Example 1 in the same amount as the compound A as thesolid content to obtain a photocurable composition of ComparativeExample 1.

The above photocurable composition was subjected to the same proceduresas in Example 1 to obtain a photocurable resist film on the epoxy resinbase.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [line (μm)/space (μm)] in an irradiation dose of 3 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 60° C. for 10minutes, dipping into a 1% sodium carbonate aqueous solution at 30° C.for one minute to carry out an alkali developing treatment for removingthe non-cured area of the photocurable resist film, carrying out etchingby dipping into an aqueous 24% ferric chloride solution for 2 minutes,resulting in that separation of the resist film during etching made itimpossible to obtain a resolution of 100 μm/100 μm.

Comparative Example 2

Example 1 was duplicated except that the following water-solublephotocurable resist composition was used in place of thephotopolymerizable polyurethane compound A in Example 1 in the sameamount as the compound A as the solid content to obtain a photocurablecomposition of Comparative Example 2.

The water-soluble photocurable resist composition was prepared by aprocess which comprises charging a mixture of 334 parts of polyesterdiol(polymethylpentane adipate, marketed by Kuraray Co., Ltd., numberaverage molecular weight: 2000), 24.3 parts of glycerol monoacrylate,44.7 parts of 2,2-dimethylol propionic acid, 0.52 part of hydroquinonemonomethyl ether, and 0.26 part of dibutyltin dilaurate, heating at 40°C. adding 185 parts of isophorone diisocyanate with agitationintroducing a dry air, heating at 80° C. for reacting for 6 hours toobtain an intermediate having an isocyanate group content of 1.30% byweight, adding 34.8 parts of 2-hydroxyethyl acrylate, reacting at 80° C.for 15 hours to obtain an urethane resin containing a radicallypolymerizable unsaturated group having an isocyanate group content of0.16% by weight and an anionic, hydrophilic group, cooling down to 40°C., adding 33.7 parts of triethylamine, uniformly mixing with agitationto form a resin solution, introducing the resin solution into a fiveliter four-necked flask charged with 1503 parts of deionized water at50° to make water-soluble, and subjecting to desolvating of methyl ethylketone under vacuum to obtain a light yellow, transparent,water-soluble, photocurable resin solution having a nonvolatile contentof 30% by weight.

The water-soluble photocurable resist composition obtained as above wassubjected to the same procedures as in Example 1 to obtain aphotocurable resist film.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [line (μm)/space (μm)] in an irradiation dose of 3 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 60° C. for 10minutes, and dipping into a 1% sodium carbonate aqueous solution at 30°C. for one minute to carry out an alkali developing treatment forremoving the non-cured area of the photocurable resist film, withoutobtaining a satisfactorily cured resist film.

Comparative Example 3

Example 1 was duplicated except that the following photocurable resinsolution was used in place of the photopolymerizable polyurethanecompound A in Example 1 in the same amount as the compound A as thesolid content to obtain a photocurable composition of ComparativeExample 3.

The photocurable resin was prepared by a process which comprises heatinga mixture of 134 parts of dimethylol propionic acid, 366 parts ofε-caprolactone and 0.15 part of stannous chloride, reacting for about 10hours, cooling down to 60° C., adding 333.4 parts of isophoronediisocyanate and, as a diluent, 409.4 parts of polyethylene glycoldiacrylate (marketed by Nippon Kayaku Co., Ltd., Kayarad PEG400DA, tradename), reacting at 80° C. for about 10 hours, adding 121.8 parts of2-hydroxyethyl acrylate and 0.6 part of p-methoxyphenol, and reacting at80° C. for about 15 hours to obtain an urethane acrylate containing 30%of polyethylene glycol diacrylate.

The above photocurable composition was subjected to the same proceduresas in Example 1 to obtain a photocurable resist film.

A visible light laser was irradiated onto the photocurable resistfilm-formed epoxy resin base so as to result a resolution of 100 μm/100μm [line (μm)/space (μm)] in an irradiation dose of 5 mj/cm² by use of a488 nm wave length argon ion laser irradiation apparatus, followed byheating the photocurable resist-formed epoxy resin base at 600° C. for10 minutes, and dipping into a 1% sodium carbonate aqueous solution at30° C. for one minute to carry out an alkali developing treatment forremoving the non-cured area of the photocurable resist film, withoutobtaining a satisfactorily cured resist film.

Comparative Example 4

A mixture of 40 parts of methyl methacrylate, 40 parts of butylacrylate, 20 parts of acrylic acid and 2 parts of azobisisobutyronitrilewas dropped into 90 parts of propylene glycol monomethyl ether at 110°C. over 3 hours under nitrogen atmosphere. Completion of dropping wasfollowed by aging for one hour, dropping a mixture of one part ofazobisdimethylvaleronitrile and 10 parts of propylene glycol monomethylether over one hour, aging for 5 hours to obtain a high acid valueacrylic resin (resin acid value: 155 mgKOH/g) solution, adding 24 partsof glycidyl methacrylate, 0.12 part of hydroquinone and 0.6 part oftetraethylammonium bromide, and reacting at 110° C. for 5 hoursintorducing air to obtain a photocurable resin solution having a solidcontent of about 55.4%. The resulting resin had a resin acid value ofabout 50 mgKOH/g and a number average molecular weight of about 20,000.

Example 3 was duplicated except that the above photocurable resinsolution was used in place of the photopolymerizable polyurethanecompound A in Example 3 in the same amount as the compound A as thesolid content to obtain a photocurable composition of ComparativeExample 4.

The above photocurable resist composition was subjected to the sameprocedures as in Example 3 to obtain a photocurable solder resist film.

The photocurable composition obtained as above was coated by a barcoater onto a copper-clad glass fiber-reinforced epoxy resin base havinga copper layer of 18 μm on its surface, a base thickness of 2 mm and asize of 350×460 mm, followed by drying at 80° C. for 10 minutes toobtain a photocurable resist film having a dry film thickness of 50 μm.

A light was irradiated onto the photocurable resist film-formed epoxyresin base so as to result a resolution of 100 μm/100 μm [line(μm)/space (μm)] in an irradiation dose of 100 mj/cm² by use of anultrahigh pressure mercury lamp, followed by dipping into a 1% sodiumcarbonate aqueous solution at 30° C. for one minute to carry out analkali developing treatment for removing the non-cured area of thephotocurable resist film, resulting in producing a remainingphotocurable resist film without being removed, and in making itimpossible to obtain a resist pattern having a resolution of 100 μm/100μm.

Effect of the Invention

Thus, the present invention provides such remarkable effects (1) that anarrow molecular weight distribution provides a uniform solubility in analkali developing solution and good anti-etching resistance to theetching solution, (2) that ensured introduction of carboxyl group intothe resin provides a uniform solubility in the alkali developingsolution and good anti-etching resistance to the etching solution, (3)that presence of polyurethane linkage provides good coating filmproperties and good anti-etching resistance, and that (4) the absence ofthe basic compound such as an amine and the like as the neutralizingagent in the molecule results good properties in anti-alkali developingproperties and anti-etching properties in the exposed area.

Applicability in the field

The organic solvent based photocurable resist composition of the presentinvention is applicable to a solder resist, etching resist, anti-platingresist, etc.

What is claimed is:
 1. An organic solvent based photocurable resistcomposition containing a photopolymerizable polyurethane compound havinga repeating unit represented by the following formula:B—[X]_(n)[Y]_(m)—B, where X is represented by the formula:

and Y is represented by the formula: —OOCHN—A—NHCOO—(R₂)—, A is astructural unit derived from a polyisocyanate compound, B is same ordifferent and a structural unit derived from a hydroxy compound havingat least one photopolymerizable unsaturated group at molecular terminalsrespectively, R₁ is a structural unit derived from dimethylol butyricacid, R₂ is a structural unit derived from a polyol compound, n is aninteger of 1 to 10, m is an integer of 1 to 10, provided that at leastone X and at least one Y are optionally bonded to each other so as toform at least one X-Y bond, said composition being dissolved ordispersed into an organic solvent, in use.
 2. A method of forming aresist pattern comprising the following steps: (1) coating the organicsolvent based photocurable resist composition as claimed in claim 1 ontoa substrate to form a photocurable resist film, (2) exposing thephotocurable resist film directly to a visible light laser beam forcuring so that a resist film having a predetermined printed image can beformed; and (3) subjecting the resist film formed in the step (2) to analkali developing treatment to form a resist pattern on the substrate.3. A composition as claimed in claim 1, wherein B is a structural unitderived from a hydroxy compound having two photopolymerizableunsaturated groups at molecular terminals respectively.
 4. A compositionas claimed in claim 1, wherein said composition contains a titanocenecompound as a polymerization initiator.
 5. A composition as claimed inclaim 1, wherein said composition contains a photosensitizer.
 6. Acomposition as claimed in claim 3, wherein said composition contains atitanocene compound as a polymerization initiator.
 7. A composition asclaimed in claim 3, wherein said composition contains a photosensitizer.